Bug 1417264 - Write objdir .mozconfig from Python; r=nalexander

This is a pretty straightforward port of the logic. But we
even go a step further: we delete the file in the objdir if there is
no source mozconfig!

MozReview-Commit-ID: AHFFzy6mXRY

client.mk

@@ -138,7 +138,6 @@ configure-files: $(CONFIGURES)
 
 configure-preqs = \
   configure-files \
-  save-mozconfig \
   $(OBJDIR)/.mozconfig.json \
   $(NULL)
 
@@ -151,11 +150,6 @@ endif
 
 $(OBJDIR)/.mozconfig.json: ;
 
-save-mozconfig: $(FOUND_MOZCONFIG)
-ifdef FOUND_MOZCONFIG
-	-cp $(FOUND_MOZCONFIG) $(OBJDIR)/.mozconfig
-endif
-
 configure:: $(configure-preqs)
 	$(call BUILDSTATUS,TIERS configure)
 	$(call BUILDSTATUS,TIER_START configure)

python/mozbuild/mozbuild/controller/building.py

@@ -4,6 +4,7 @@
 
 from __future__ import absolute_import, unicode_literals
 
+import errno
 import getpass
 import io
 import json
@@ -1371,6 +1372,19 @@ def _run_client_mk(self, target=None, line_handler=None, jobs=0,
         with FileAvoidWrite(mozconfig_mk) as fh:
             fh.write(b'\n'.join(mozconfig_filtered_lines))
 
+        # Copy the original mozconfig to the objdir.
+        mozconfig_objdir = os.path.join(self.topobjdir, '.mozconfig')
+        if mozconfig['path']:
+            with open(mozconfig['path'], 'rb') as ifh:
+                with FileAvoidWrite(mozconfig_objdir) as ofh:
+                    ofh.write(ifh.read())
+        else:
+            try:
+                os.unlink(mozconfig_objdir)
+            except OSError as e:
+                if e.errno != errno.ENOENT:
+                    raise
+
         if mozconfig_make_lines:
             self.log(logging.WARNING, 'mozconfig_content', {
                 'path': mozconfig['path'],